The present invention relates to the video processing system art. It finds particular application in conjunction with a method and apparatus for removing a checkerboard-like noise artifact from a captured composite NTSC video frame. However, it should be appreciated that the present invention may also find application in conjunction with other types of video processing systems and applications that input composite NTSC video signals.
The NTSC video standard is used in the United States and Japan. This standard specifies a signal transmission at 525 scanning lines per video frame transmitted at a rate of 30 frames per second. Each video frame consists of two interlaced fields F1 and F2 that alternate at 60 times per second. The composite NTSC video signal can be represented as:
u(x,y,t)=Y(x,y,t)+I(x,y,t) cos(2xcfx80fsx+"PHgr") cos[xcfx80(frtxe2x88x92f1y)]+Q(x,y,t) sin(2xcfx80fsx+"PHgr")cos[xcfx80(frtxe2x88x92f1y)],xe2x80x83xe2x80x83Eq. 1
where Y and (I, Q) are the luminance and the chrominance components, respectively; fs is the color subcarrier frequency; and f1 an fr are the scan line and the frame frequencies, respectively.
Capturing still or freeze-frame pictures from a composite NTSC video signal for viewing on a progressive monitor, printing on a printer, inserting into an electronic document, etc. is a challenging problem in the area of video processing. Artifacts that may go unnoticed when looking at a moving video signal become extremely objectionable when viewing as a still picture.
In particular, when a composite NTSC video signal is captured, such as with a SUN Parallax video capture board, a checkerboard-like noise artifact can be observed on the vertical and diagonal edges in the captured video frame. The checkerboard-like artifact occurs in each of the interlaced fields (F1, F2) of the captured video frame. It is suggested that the checkerboard-like noise artifact may be a result of the quadrature demodulation and the corresponding chrominance shifts due to phase detection errors combined with the aliasing caused by the sampling of the color components during the process of A/D conversion.
Accordingly, it has been considered desirable to develop a new and improved method and apparatus for removing checkerboard-like noise artifact from a captured composite NTSC video frame that meets the above-stated needs and overcomes the foregoing difficulties and others while providing better and more advantageous results.
In accordance with one aspect of the present invention, a method of removing an artifact from a video frame captured from a moving video signal is disclosed. The video frame includes of a plurality of pixel elements stored in a buffer. The method includes the steps of a) determining whether a first pixel element is associated with an artifact in the video frame; and b) adjusting the first pixel element based on at least a second pixel element if it is determined that the first pixel element is associated with an artifact in the video frame.
In accordance with another aspect of the present invention, a method of processing a video frame captured from a moving video signal is disclosed. The video frame includes a plurality of pixel elements stored in a first buffer. The method includes the steps of a) accessing a first pixel element from the first buffer; b) determining whether the first pixel element is associated with an artifact in the video frame based on values of a first plurality of pixel elements including a value of the first pixel element; c) determining an adjusted value of the first pixel element based on values of a second plurality of pixel elements including the value of the first pixel element when the first pixel element is associated with an artifact in the video frame; d) storing the adjusted value of the first pixel element in a second buffer when the first pixel element is associated with an artifact in the video frame, otherwise storing the value of the first pixel element in the second buffer; and e) repeating steps a)-d) for a plurality of pixel elements associated with the video frame to generate a filtered video frame in the second buffer.
In yet another embodiment of the present invention a method of processing a video frame captured from a moving video signal is disclosed. The video frame includes a first plurality of pixels forming a first interlaced video field and a second plurality of pixels forming a second interlaced video field. The method includes the steps of a) determining whether a first pixel of the first field is associated with an artifact in the video frame; b) adjusting the first pixel of the first field based on at least a second pixel of the first field if it is determined that the first pixel of the first field is associated with an artifact in the video frame; c) determining whether a first pixel of the second field is associated with an artifact in the video frame; and d) adjusting the first pixel of the second field based on at least a second pixel of the second field if it is determined that the first pixel of the second field is associated with an artifact in the video frame.
One advantage of the present invention is the provision of a new method for removing a checkerboard-like noise artifact from a captured composite NTSC video frame without blurring the edges of images within the video frame.
Another advantage of the present invention is the provision of an improved method for removing a checkerboard-like noise artifact from a captured composite NTSC video frame without blurring the edges of images within the video frame.
Yet another advantage of the present invention is the provision of a new apparatus for removing a checkerboard-like noise artifact from a captured composite NTSC video frame without blurring the edges of images within the video frame.
Still another advantage of the present invention is the provision of an improved apparatus for removing a checkerboard-like noise artifact from a captured composite NTSC video frame without blurring the edges of images within the video frame.
Still further advantages of the present invention will become apparent to those of ordinary skill in the art upon reading and understanding the following detailed description of the preferred embodiment.